The placenta shows a real affinity for some
toxic substances; in it accumulate copper and mercury, but not
lead, and it is therefore through it that the poison reaches the
fetus; in addition to its pulmonary, intestinal, and renal
functions, it fixes glycogen and acts as an accumulator of
poisons, and so resembles in its action the liver; therefore the
organs of the fetus possess only a potential activity. The
storing up of poisons in the placenta is not so general as the
accumulation of them in the liver of the mother. It may be asked
if the placenta does not form a barrier to the passage of poisons
into the circulation of the fetus; this would seem to be
demonstrated by mercury, which was always found in the placenta
and never in the fetal organs. In poisoning by lead and copper
the accumulation of the poison in the fetal tissues is greater
than in the maternal, perhaps from differences in assimilation
and disassimilation or from greater diffusion. Whilst it is not
an impermeable barrier to the passage of poisons, the placenta
offers a varying degree of obstruction: it allows copper and lead
to pass easily, arsenic with greater difficulty. The accumulation
of toxic substances in the fetus does not follow the same law as
in the adult.
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